Composite powders and apparatus for the production of the same



Feb. 18, 1969 "r. WEBER 3,428,543

COMPOSITE POWDERS AND APPARATUS FOR THE PRODUCTION OF THE SAME Filed May'7, 1965 United States Patent U.S. Cl. 204-273 Int. Cl. B01k 3/00 4Claims ABSTRACT OF THE DISCLOSURE A composite powder consistingessentially of a core of tungsten, titanium or the carbides, borides,silicides, nitrides and oxides of tungsten or titanium and an envelopeelectrodeposited thereon, said envelope being nickel, cobalt, copper orsilver; and an apparatus for preparing said composite powders.

This invention relates to composite powders and to processes andapparatus for the production of the same.

A composite powder within the meaning of the invention is a powder, theindividual grains of which consist of two or more components which,without being chemically bonded, cannot be readily separatedmechanically. Such is the case, more particularly, when one componentcompletely surrounds the other component, in which arrangement onecomponent is called the core, while the other one is called the envelopeor jacket.

Such materials are used in powder metallurgy and in the field offlame-spraying.

An important advantage of such arrangements over similarly composedmixtures resides in the fact that they cannot separate into theirdifferent components when they are handled. The contact between the twophases (envelope/ core) is very intimate and the surfaces of contact aremaximal. Another important advantage when compared with alloys residesin the fact that the heat of formation in the composite powder ispreserved and becomes free and can be utilized only during subsequentthermal processing. Moreover, composite powders make it possible, forexample, to overcome difficulties of wetting, to prevent agglomerationsduring dispersion and to obtain greater molding strengths.

In a known process for the production of composite powders, the envelopeis applied to the core by hydrogen pressure reduction of thecorresponding ammoniacal metallic salt solution.

It has now been found that it is possible to apply the envelopes to thecores electrolytically, i.e., by means of a process similar to the onewhich is used in galvanotechniques (electroplating) in the production ofcorresponding bulk goods.

The essential differences with respect to the last-named process residein the fact that the individual particles are incomparably smaller thanthe bulk goods and need not necessarily be metals.

The envelope materials used according to the invention are all metalswhich can be electrolytically separated from aqueous solution,preferably Ni, Co, Cu, and Ag. The materials used for the core arepreferably metallic powders, as well as powders of carbides, borides,silicides, and suitable oxides, which do not react with the electrolyte.Solutions similar to those used in galvanotechniques are used aselectrolytes. The electrolytes are selected depending on the compositionof the composite powder desired.

The anode material used is the material of the desired envelope.Insoluble anode material, such as, for example, platinized titanium, isalso suitable as anode material; however, in this case the electrolytemust be constantly renewed.

It is essential for the process according to the invention that thematerial be constantly turned, either continuously or discontinuously,that it be possibly not in suspension during the current flow, and thatthe cathode surface remain covered with powder almost completely anduniformly during the electrolysis.

A tank with a cathodically connected metallic bottom, for example,nickel is used for the electrolysis. The anode comprises holes to allowthe escape of possibly evolving gases and is suspended in the tankparallel to the bottom thereof.

The apparatus provided with an automatic turning device, comprises aplastic plate, which will be described below, between the anode andcathode. If the operation is a discontinuous one, the turning iseffected in that the current is disconnected and the anode is liftedout, and then the material is turned by hand and is uniformlydistributed over the bottom.

The operation proceeds as follows: the core material is uniformlydistributed at the bottom, whereupon the automatic turning device isintroduced, the anode being suspended thereabove. Suitable electrolytesolution is then added in an amount such that the anode is completelycovered. After the automatic turning device has been connected, thevoltage is applied to the cell.

The duration and intensity of the current flow depends on the desiredcomposition of the composite powder and on the resistance of the bath.

After the electrolysis is terminated, the electrolyte is siphoned off,the composite powder is conveyed onto a suction filter and is washed ina suitable manner. After drying, the material obtained in this manneris, in general, the finished composite powder. If the composite powderis to have a specific grain size distribution, it must be screened inthe usual manner. Oversized grain, caused partially by the naturalincrease of the diameter due to one layer being covered with another,and partially to the fact that several grains are covered together, canbe ground to the desired grain or particle size.

In the case of some core materials, not every grain is covered. Thisdifficulty can subsequently be overcome, for example, when nickel andcobalt are used as the envelope material, in that a subsequent magneticseparation and demagnetization is carried out.

The invention will be more readily understood from the followingdetailed description of a preferred embodiment as illustrated in theaccompanying drawing in which:

FIGURE 1 is a side view partly in section of a cell provided inaccordance with the invention; and

FIGURE 2 is a top plan view of one of the components of the cell.

The accompanying drawing shows an electrolyzing cell according to theinvention with automatic turning device or apparatus. The insidediameter of the tank amounts, for example, to 40 cm.

The process is carried out in the following manner:

After the electrolyzing cell 1 has been charged, as -described above,the automatic turning device 5, which is a perforated plastic disc orplate, is caused to start to rotate slowly (for example, 0.5 to 6revolutions per minute) by means of a motor 3 with gear 4 arrangedadjustably on a vertical holding rod 2.

For this purpose, the disc is held in position by a drive rod 6 arrangedin the center of the disc and extending perpendicularly to said disc.For insulating purposes the rod 6 is covered with a plastic layer orcoating 7. The rod 6 can be connected to the motor shaft 9 by way of acoupling member 8.

In the manner of a Nipkow disc, non-conductive plastic pins 10, disposedalong a figure S, are driven into the non-conductive plate 5. Said plate5, provided with holes 18, is fitted with very little play in the tank11 of the electrolyzing cell 1.

During the operation, the pins just contact the bottom 13 of the tank11, said bottom being connected to the cathode 12. An insulating plasticplate 15 is arranged between the bottom 13 and a base plate 14.

Due to said arrangement, each increment of the bottom 13 is contactedonce during each revolution and the material is turned.

Arranged above the plastic plate 5 is the anode 16 which, as alreadystated, is a perforated disc which is provided in its center with a bore17, through which the rod 6 of the plastic disc is guided with play. Theanode is suspended in the tank 11 by means of a suspension 19.

Example 1 The powder desired is a composite powder consisting oftungsten carbide and 12% Co having a grain size of 4080 The startingmaterial is a tungsten carbide, grain size 37 to 70 of which 2.5 kg. areused. The electrolyte is a solution of 60 g. of cobalt sulfate per literand 150 g. of ammonium sulfate per liter, which is adjusted to a pH ofabout 7 with ammonia. The amperage amounts to 48 amp the voltage will beapproximately 2 volts. Electrolysis is carried out for 6.50 hours. AfterWashing and drying, about 2800 g. of composite powder are extracted. 2.5kg. thereof pass through a suitable screen; the remaining 300 g. areground in a ball mill for 15 minutes. After screening there remains aresidue of about 100 g. of oversize grains. The material having theright grain size is separated magnetically. Magnetic separation shows2,200 g. of strongly magnetic fractions with 12.3% C0, 120 g. of weaklymagnetic fractions with 3.6% Co, and 360 g. of non-magnetic material.After demagnetization, the strongly magnetic fraction is the desiredfinished composite powder. The remainder is used again as startingmaterial in subsequent operations.

Photomicrographs show that the tungsten carbide cores are almost 100%covered with cobalt.

Example 2 The powder desired is a composite powder consisting of atungsten core having an average grain size of 6a with a 3.5% Ni and 1.5%Cu coating. 2.5 kg. of the desired core material are used as thestarting material. First, electrolysis is carried out for two hours at48 amp with a weakly ammonical nickel-chloride solution which contains150 g. of ammonium chloride per liter. The material obtained in thismanner passes 100% through the finest screen and contains nonon-magnetic constituents. A mixture of 40 preparations had a nickelcontent of 3.4% determined analytically. The desired material iselectrolyzed for 55 minutes at 48 amp with anammonium-sulfate-containing copper sulfate solution neutralized to pH 7.The resulting material is screened through a 400 mesh screen; thereremains a residue of about 2% of high-copper containing oversized grain.The screened material of 40 preparations is mixed and has a coppercontent of 1.6% The total amount of the 40 preparations amounts to 102kg. of composite powder of the desired composition.

Example 3 The powder desired is a titanium/nickel composite powder of agrain size of 140+325 mesh with a titanium core and a nickel content of60% Ni. 400 g. of titanium powder of the grain size .200+325 mesh areused. Electrolysis is carried out with an electrolytic solution, asdescribed in Example 2, for 6 /2 hours at 48 amp.

The material is turned manually and discontinuously,

namely, about every twenty minutes, during the electrolysis. Since thelight titanium powder tends to stick to the cathode, the latter isgreased with Vaseline prior to use. The material is dried after theelectrolysis and is screened through a 200 mesh screen. The constituent200 consists mainly of titanium powder with a very small content ofnickel. The coarse fraction is ground and is screened through a 140 meshscreen. passes through the screen and is the desired composite powder.

The great number of possible components for envelope and core allows avery large amount of combinations. Thus it is impossible to quote allconceivable practical examples. In all possible combinations the methodaccording to the invention is the same. The method according to theinvention is based on a system which is not restricted either by thenature or by the number of the combinations cited in the practicalexamples. Further examples will easily fit in this system.

What is claimed is:

1. Apparatus for electrolytically applying envelopes to cores to formcomposite powder grains, said apparatus comprising a tank adapted forcontaining an electrolyte and including a bottom adapted to constitute acathode and to support said cores, anode means spaced from said bottom,perforated means between the bottom and anode means, a plurality of pinson the perforated means extending to said bottom and being arranged suchthat, on rotation of the perforated means substantially the entirebottom is traversed by the pin-s, and means connected to the perforatedmeans for rotating the latter.

2. Apparatus for electrolytically applying envelopes to cores to formcomposite powder grains, said apparatus comprising a tank adapted forcontaining an electrolyte and including a bottom adapted to constitute acathode and to support said cores, anode means spaced from said bottom,a perforated disc between the bottom and anode means, a plurality ofpins arranged generally diametrically on the disc and disposed generallyas to constitute a figure S, said pins extending to said bottom andbeing arranged such that, on rotation of the disc, substantially theentire bottom is contacted by the pins, and means extending through theplate and connected to the disc for rotating the latter.

3. Apparatus comprising a tank adapted for containing an electrolyte andincluding a bottom adapted to constitute a cathode and to support amaterial to be treated, a plate having an opening therein and arrangedin parallel to said bottom, said plate being of a material insoluble insaid electrolyte, electrically conductive means suspending the plate inthe tank such that said plate constitutes an anode, a perforated discbetween the bottom and plate, a plurality of pins arranged generallydiametrically on the disc and disposed generally to constitute a figureS, said pins extending to said bottom and being arranged such that, onrotation of the disc, substantially the entire bottom is traversed bythe pins, and means extending through the plate and connected to thedisc for rotating the latter.

4. Apparatus for electrolytically applying envelopes to cores to formcomposite powder grains, said apparatus comprising a tank adapted forcontaining an electrolyte and including a bottom adapted to constitute acathode and to support said cores, a plate having an opening therein andarranged in parallel to said bottom, said plate being of a materialinsoluble in said electrolyte, electrically conductive means suspendingthe plate in the tank such that said plate constitutes an anode, aperforated disc between the bottom and plate, a plurality of pinsarranged generally diametrically on the disc and disposed genreally asto constitute a figure S, said pins extending to said bottom and beingarranged such that, on rotation of the disc, substantially the entirebottom is traversed by the pins, and means extending through the plateand connected to the disc for rotating the latter whereby cores on thebottom are turned for complete processing, said means including a driverod connected to the disc and an insulating coating on said rod.

References Cited UNITED STATES PATENTS Huber et a1. 204-10 Aylsworth204-36 Crane 204-23 Taylor 204-36 Welch 204-23 Harshaw 204-23 Wulif209-214 Matskawa 204-23 6 FOREIGN PATENTS 4/ 1952 Great Britain.

OTHER REFERENCES 5 Handbook of Practical Electroplating, Thomas M.Rodgers, Macmillan Company, New York, 1959, p. 237.

ROBERT K. MIHALEK, Primary Examiner.

10 T. TUFARIELLO, Assistant Examiner.

U.S.Cl. X.R.

